Intestinal epithelia cells express unique gene products which enable the intestine to perform specialized tasks including the absorption and processing of nutrients. Enterocyte function varies during development, along the length of the intestinal tract (horizontal axis), along the crypt-villus unit (vertical axis), in response to physiological stimuli, and in disease states. This complex pattern of function is directly related, in many cases, to the pattern of expression of intestine-specific genes that encode proteins which perform those functions. Little is known about the molecular mechanisms which regulate patterns of intestine- specific gene transcription or intestinal epithelial cell development and differentiation. In this proposal, sucrase-isomaltase (SI) will be used as a model gene to probe the molecular mechanisms which regulate enterocyte- specific gene transcription. SI has been chosen because it is enterocyte- specific, expressed at moderately high levels, has a complex pattern of developmental and adult expression, is altered in physiological and disease states, and is expressed in intestinal tumor cell lines which enables in vitro experimental approaches. The reagents required for these studies have been developed including human and mouse SI CDNAS and genomic clones containing the 5'-flanking regions of both the human and mouse SI genes. Transfection experiments have demonstrated that the human SI gene contains elements capable of directing intestine-specific transcription an transgenic mice containing a human SI gene construct have been made. Therefore, the goals of this proposal are: 1) To identify DNA regulatory regions in the SI gene and the corresponding sequence-specific nuclear binding proteins which are necessary to direct efficient, enterocyte- specific transcription, and 2) To determine which DNA regulatory regions are required to recapitulate the spatial (horizontal and vertical) and developmental patterns of SI gene expression in adult tissues using transgenic mice. The experiments outlined in this proposal use a multifaceted approach to provide detailed information on the regulation of SI gene transcription. Elucidation of transcriptional mechanisms for tissue-specific genes in other tissues has led to identification of DNA binding proteins which direct cell-specific transcription and are important for cellular differentiation and proliferation. Thus, SI DNA elements and/or nuclear binding proteins may participate in the regulation of multiple intestinal genes, in the process of differentiation and development, or serve to regulate proliferation. The anticipated result of these studies will be a better understanding of the molecular mechanisms which regulate intestinal gene expression, development, and differentiation.